Conductive polymer comprising 3,6-carbazole and organic solar cell using same

ABSTRACT

The present invention relates a conductive polymer containing a 3,6-carbazole group represented by Chemical Formula 1 
     
       
         
         
             
             
         
       
     
     and an organic polymer thin film solar cell including the same.

TECHNICAL FIELD

The present invention relates to a conductive polymer containing 3,6-carbazole and an organic solar cell device using this conductive polymer as a photoelectric conversion material, and in particular, relates to preparing a conductive polymer that has improved hole mobility by adding more than a certain amount of 3,6-carbazole to the conductive polymer, and an organic solar cell device that improves energy conversion efficiency by using this conductive polymer as a photoelectric conversion material.

BACKGROUND ART

Studies on solar cells using an organic polymer have been extensively carried out since Heeger of UCSB first showed the possibility of a solar cell using an organic polymer in 1992. A solar cell using an organic polymer is a heterojunction thin film device in which a light-absorbing organic polymer and a C₆₀ fullerene derivative or C₇₀ fullerene derivative having high electron affinity are mixed, and uses indium tin oxide (ITO), which is a transparent electrode, as an anode, and a metal electrode such as an A1 electrode, which has low work function, as a cathode. Electron-hole pairs or excitons are formed when a photoactive layer formed with an organic polymer absorbs light. These electron-hole pairs or excitons move to the interface of the copolymer and the C₆₀ fullerene derivative or C₇₀ fullerene derivative, are separated into electrons and holes, and then the electrons move to the metal electrode and the holes move to the transparent electrode resulting in the generation of electrons. Currently, the efficiency of an organic polymer thin film solar cell using an organic polymer reaches 6.5 to 7.0% (Science, 2007, 307, 222-225).

However, current efficiency of organic polymer solar cells is still low compared to the maximum efficiency (˜39%) of solar cells using silicon. Therefore, there have been demands for the development of organic polymer solar cells having higher efficiency.

Recently, Korean Patent Application Laid-Open Publication No. 2010-0111767 disclosed a conductive polymer that includes 2,7-carbazole in the main chain and an organic solar cell using this conductive polymer. An objective is to improve the efficiency of the solar cell by the conductive polymer that includes 2,7-carbazole in the main chain improving the light absorption and the hole mobility. However, despite the use of 2,7-carbazole, the hole mobility are relatively low compared to the electron mobility, therefore, there have been a problem that luminous efficiency is not readily improved.

DISCLOSURE Technical Problem

An objective of the present invention is to provide a novel conductive copolymer that can prepare a highly efficient solar cell in which the hole mobility is similar to the electron mobility.

Another objective of the present invention is to provide a highly efficient solar cell in which the hole mobility is similar to the electron mobility, and a preparation method thereof.

Still another objective of the present invention is to provide a highly efficient photoelectric conversion device in which the hole mobility is correspondently high compared to the electron mobility, and a preparation method thereof.

Technical Solution

The present invention provides a copolymer containing a 3,6-carbazole group represented by the following Chemical Formula 1.

Herein, Y is an electron acceptor, X is an electron donor, and R₁ is independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl, C₁-C₂₀ heteroaryl, CN, C(O)R, or C(O)OR and R is independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl or C₁-C₂₀ heteroaryl. For l and m, l+m=1 in a molar fraction and m has a range of 0.01≦m≦0.9, the molecular weight has a range of 5,000≦Mn≦100,000, and the degree of polymerization preferably ranges from 5 to 200.

In the present invention, when the content of the 3,6-carbazole group is excessive, it is difficult to expect high light absorption of the conductive polymer due to the characteristics of a carbazole group having relatively low absorbance. Therefore m preferably has a range of 0.01≦m≦0.7, more preferably has a range of 0.01≦m≦0.5, and most preferably has a range of 0.01≦m≦0.1.

In the present invention, the copolymer of Chemical Formula 1 is a conductive copolymer, and has a structure in which a bonding structure of 3,6-carbazole having high hole mobility and an electron acceptor (Y) is irregularly arranged in an electron acceptor (Y)-electron donor (X) bonding structure as a second electron donor.

In the present invention, as the electron acceptor (Y) and the electron donor (X), typical electron acceptors and electron donors known in organic solar cells may be used. In the present invention, the electron acceptor Y is a carbon-based aromatic compound having 10 or more carbon atoms, or a heterogeneous aromatic compound including sulfur, phosphorous, nitrogen or selenium, and may have a substituent capable of increasing the solubility of the polymer. In preferable embodiments of the present invention, as the electron acceptor (Y), one, two or more types may be selected among the compounds of the following Chemical Formula (2), and used.

Herein, R₄ or R₅ is C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, aryl, heteroaryl, CN, C(O)R or C(O)OR, and R is C₁-C₂₀ alkyl, C₁-C₂₀ heterocycloalkyl, aryl or heteroaryl.

In the present invention, as the preferable electron donor X, one, two or more types among the compounds of the following Chemical Formula (3) may be used.

Herein, R₂ or R₃ is C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl, C₁-C₂₀ heteroaryl, CN, C(O)R or C(O)OR, and R is C₁-C₂₀ alkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl or C₁-C₂₀ heteroaryl.

Although it is not limited theoretically, hole mobility significantly increases when 3,6-carbazole is introduced since a nitrogen atom, which stabilizes holes, is included in the conjugation of the main chain (Macromolecules 2011, 44(7), 1909-1919), and as a result, the efficiency of a solar cell increases since the hole mobility and the electron mobility of the organic thin film solar cell are balanced. This phenomenon cannot be expected for existing copolymers that includes 2,7-carbazole since a nitrogen atom is not included in the conjugation when the 2,7-carbazole is included in the main chain.

Another aspect of the present invention provides an organic solar cell using a conductive copolymer containing a 3,6-carbazole group.

As in Korean Patent Application Laid-Open Publication No. 2010-0111767, which is introduced as a reference document in the present invention, an organic solar cell in one preferable example includes a substrate, a first electrode, a photoelectric conversion layer and a second electrode, and in the photoelectric conversion layer, a conductive polymer containing a 3,6-carbazole group represented by Chemical Formula 1 is used as an electron donor, and a C₆₀ fullerene derivative or a C₇₀ fullerene derivative may be mixed thereto as an electron acceptor. A buffer layer may be further introduced between the photoelectric conversion layer and the first electrode, and an electron transfer layer, a hole blocking layer or an optical space layer may be further introduced between the photoelectric conversion layer and the second electrode.

Transparent materials are preferable as the substrate, and as one example, glass, polyethylene terephthalate (PET), polyethylene naphthelate (PEN), polypropylene (PP), polyamide (PI), triacetyl cellulose (TAC) or the like may be used. In addition, the first electrode may be formed by either applying transparent materials or by coating in the form of a film using methods such as sputtering or spin coating on one surface of the substrate. The first electrode is a part functioning as an anode, and materials thereof are not particularly limited as long as the material has transparency and conductivity with small work function compared to the second electrode, and preferable examples thereof include indium-tin oxide (ITO), fluorine doped tin oxide (FTO), ZnO—(Ga₂O₃ or Al₂O₃), SnO₂—Sb₂O₃, and the like, and more preferably, ITO is used. As the buffer layer formed on the first electrode, polystyrenesulfonate doped poly(3,4-ethylenedioxythiophene) [PEDOT:PSS] may be used, and may be introduced to further improve the hole mobility.

As the photoelectric conversion material of the photoelectric conversion layer, it is preferable that a conductive polymer containing a 3,6-carbazole group represented by Chemical Formula 1 and a C₆₀ fullerene derivative or a C₇₀ fullerene derivative be mixed in the mixing ratio ranging from 1:0.5 to 1:4 in a weight ratio. At this time, when the fullerene derivative is mixed in less than 0.5 weight ratio with respect to the conductive polymer containing carbazole of the present invention, the content of the crystallized fullerene derivative is insufficient, which causes difficulties in the movement of the generated electrons, and when mixed in greater than 4 weight ratio, the amount of the light-absorbing conductive polymer relatively decreases, therefore, efficient absorption of light cannot be accomplished, which is not preferable. The solution in which the photoelectric conversion material is dissolved is formed as the photoelectric conversion layer to a thickness of approximately 70 nm or more, and preferably ranging from 80 to 200 nm by being applied or coated using one method selected from a spin coating method, a screen printing method, an inkjet printing method and a doctor blade method. The second electrode may be laminated on the photoelectric conversion layer by vacuum thermal depositing a metal material such as aluminum to a thickness of 100 to 200 nm on the photoelectric conversion layer under vacuum. The material that can be used as the second electrode includes gold, aluminum, copper, silver or alloys thereof, a calcium/aluminum alloy, a magnesium/silver alloy, and the like.

Still another aspect of the present invention provides a photoelectric conversion material for an organic photovoltaic device, an organic light emitting diode or an organic thin film transistor, which includes a conductive polymer containing a 3,6-carbazole group represented by Chemical Formula 1, and an electron acceptor such as a C₆₀ fullerene derivative or a C₇₀ fullerene derivative.

Advantageous Effects

First, in the present invention, efficiency improvement of a device can be accomplished by adding a small amount of 3,6-carbazole having favorable hole mobility to all conductive copolymers used in various types of existing photoelectric conversion devices.

Second, a conductive polymer in which the carbazole compound of the present invention is introduced can be used as an electron donor in an organic photovoltaic device, and can be also used in various areas of organic electronic materials of an organic thin film transistor (OTFT), an organic light emitting diode (OLED), and the like.

Third, by providing an organic photovoltaic device that uses the conductive polymer, in which the carbazole compound of the present invention is introduced, as an electron donor, high photoelectric conversion efficiency of an organic thin film solar cell can be accomplished.

DESCRIPTION OF DRAWINGS

FIG. 1 is a graph comparing hole conductivity according to one example of the present invention.

FIG. 2 is a current-voltage graph according to one example of the present invention.

FIG. 3 is a graph comparing electron-hole mobility according to one example of the present invention.

MODE FOR DISCLOSURE

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

EXAMPLE Hole Conductivity Comparison for 3,6-Carbazole- and 2,7-Carbazole-Based Conductive Copolymer

As in Reaction Formula (1), after 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (200 mg, 0.304 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (139 mg, 0.304 mmol) were dissolved in dried toluene (10 ml), 20% tetraammonium hydroxide solution (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto. The mixture was reacted for 48 hours at 85° C. After the polymerization was complete, the result was polymerized using phenylboronic acid (10 mg) and bromobenzene (1 ml). The reaction product was poured into methanol (200 ml), the precipitate was filtered and then extracted with acetone and hexane/chloroform, and 95.2 mg of Polymer 1, which was a product, was obtained.

Mn=4,500, Mw=6,100, PDI=1.36

¹H-NMR (500 MHz, 130° C., ODCB-d₄, ppm): δ 8.53-7.01 (m, 12H); 4.58 (br, 1H); 2.31 (br, 2H); 2.00 (br, 2H); 1.18 (br, 24H); 0.77 (m, 6H).

In addition, as in Reaction Formula (2), after 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (200 mg, 0.304 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (139 mg, 0.304 mmol) were dissolved in dried toluene (10 ml), 20% tetraammonium hydroxide solution (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto. The mixture was reacted for 48 hours at 85° C. After the polymerization was complete, the result was polymerized using phenylboronic acid (10 mg) and bromobenzene (1 ml). The reaction product was poured into methanol (200 ml), the precipitate was filtered and then extracted with acetone and hexane/chloroform, and 148 mg of Polymer 2, which was a product, was obtained.

Mn=21,000, Mw=38,500, PDI=1.83

¹H-NMR (500 MHz, 130° C., ODCB-d₄, ppm): δ 8.11 (d, J=3.5 Hz, 2H); 8.02 (d, J=8.0 Hz, 2H); 7.94 (br, 2H); 7.75 (br, 2H); 7.56 (d, J=8.0 Hz, 2H); 7.45 (d, J=4.0 Hz, 2H); 4.73 (br, 1H); 2.42 (br, 2H); 2.05 (br, 2H); 1.23 (br, 8H); 1.22 (br, 16H); 0.71 (t, J=6.5 Hz, 6H)

The hole mobility of each of the obtained materials, Product 1 and Product 2, was measured using Space Charge Limited Current (SCLC). The measured hole mobility of Polymer was 1.2×10⁻⁵ cm²V⁻¹s⁻¹, and the measured hole mobility of Polymer 2 was 3.2×10⁻⁶ cm²V⁻¹s⁻¹. As in FIG. 1 that shows the hole mobility of Polymer 1 and Polymer 2 by a diagram, Polymer 1 has hole conductivity approximately 10 times larger than Polymer 2.

Polymer Synthesis Example 1 Synthesis of Polymer 3

In a microwave reaction vial, 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (10.5 mg, 0.016 mmol), 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-fluorene (181 mg, 0.314 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were placed in dried toluene (3 ml) and 20% aqueous solution of Et₄NOH. Catalyst tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto, the mixture was reacted for 2 hours at 110° C. in a microreactor, and Polymer 3, which was a dark purple solid powder (220 mg, 99%), was obtained.

Mn=14,500, Mw=42,300, PDI=2.92

NMR (400 MHz, CDCl₃, ppm): δ 8.15-6.99 (m, 12H); 2.04 (br, 3H); 1.53 (br, 2H); 1.25 (br, 19H); 0.80 (br, 9H).

Example 2 Synthesis of Polymer 4

In a microwave reaction vial, 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (21 mg, 0.03 mmol), 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-fluorene (161 mg, 0.28 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were placed, and were reacted as in Example 1, and Polymer 4, which was a dark purple solid (220 mg, 99%), was obtained.

Mn=9,400, Mw=15,400, PDI=1.64

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.56-1.26 (m, 24H); 4.62 (br, 1H); 3.40 (m, 2H); 2.85 (s, 2H); 2.37 (m, 3H); 2.02 (m, 7H); 1.52 (br, 11H); 1.25 (br, 31H); 0.82 (br, 12H).

Example 3 Synthesis of Polymer 5

In a microwave reaction vial, 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (42 mg, 0.064 mmol), 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-fluorene (147 mg, 0.256 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were placed, and were reacted as in Example 1, and Polymer 5, which was a dark purple solid (210 mg, 94%), was obtained.

Mn=6,000, Mw=9,200, PDI=1.53

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.47-6.98 (m, 15H); 4.56 (br, 1H); 2.34 (br, 2H); 2.03 (br, 3H); 1.54 (br, 6H); 1.23 (br, 24H); 0.86 (br, 8H).

Example 4 Synthesis of Polymer 6

In a microwave reaction vial, 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (102 mg, 0.16 mmol), 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-fluorene (100 mg, 0.16 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were placed, and were reacted as in Example 1, and Polymer 6, which was a dark purple solid (210 mg, 94%), was obtained.

Mn=6,000, Mw=9,200, PDI=1.53

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.47-6.98 (m, 15H); 4.56 (br, 1H); 2.34 (br, 2H); 2.03 (br, 3H); 1.54 (br, 6H); 1.23 (br, 24H); 0.86 (br, 8H).

Comparative Example 1 Synthesis of Polymer 7

In a microwave reaction vial, after (4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-fluorene (200 mg, 0.31 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were dissolved in dried toluene (10 ml), 20% tetraammonium hydroxide solution (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto. The mixture was reacted for 2 hours at 110° C. in a microreactor. After the polymerization was complete, the result was polymerized using phenylboronic acid (10 mg) and bromobenzene (1 ml). The reaction product was poured into methanol (200 ml), the precipitate was filtered and then extracted with acetone and hexane/chloroform, and a dark purple solid (220 mg, 99%), was obtained.

Mn=18,400, Mw=43,400, PDI=2.36

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.13-6.66 (m, 12H); 2.05 (br, 2H); 1.56 (br, 7H); 1.24 (br, 3H); 1.09 (br, 12H); 0.88 (m, 2H); 0.75 (br, 5H).

Manufacture of Organic Solar Cell and Characteristics Measurements Thereof

An organic photovoltaic device was manufactured using the materials described above as an active layer. First, a substrate on which an indium tin oxide layer was applied was cleaned with a cotton swab using 2-propanol, and then cleaned with ethanol, acetone and 2-propanol for 15 minutes each in consecutive order using an ultrasonicator. After that, the substrate was treated for approximately 120 seconds using an ozone/ultraviolet light device.

Next, a poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT:PSS) polymer and 2-propanol were mixed in the ratio of 1:2 and filtered, and then deposited at 4000 rpm for 60 seconds in a spin coater, and after that, dried in an oven at 150° C. for approximately 10 minutes.

Next, a portion on which the active layer would not be deposited was cleaned using a cotton swab soaked in water, and after that, the polymerized polymer as above and C₆₀-PCBM were mixed in the ratio of 1:4, and 1 ml of dichlorobenzene was added thereto. The result was mixed for approximately 12 to 15 hours at 60 to 80° C. and filtered, and then deposited at 600 rpm for 40 seconds in a spin coater, and the device manufactured above was dried again for 30 minutes. After that, a portion that would not be used as the active layer was cleaned using a cotton swab soaked in chloroform. Next, an aluminum electrode was deposited at 5×10⁻⁶ torr using a vacuum deposition apparatus. Lastly, annealing up was carried out at a proper temperature. Hole mobility, Jsc, Voc, FF and PEC were measured for the manufactured device, and results thereof are shown in the following Table 1.

TABLE 1 Mn Hole mobility J_(sc) V_(oc) FF PCE Category Polymer (g/mol)^(a) PDI (cm²V⁻¹s⁻¹) (mA/cm²) (V) (%) (%) Example 1 Polymer 3 11,400 2.92 3.5 × 10⁻⁶ 11.6 1.0  42.4 4.9 Example 2 Polymer 4 14,500 1.64 4.1 × 10⁻⁶ 11.8 1.0  43.1 5.1 Example 3 Polymer 5 8,283 1.41 4.3 × 10⁻⁶ 9.8 0.98 44.3 4.3 Example 4 Polymer 6 9,400 1.53 1.0 × 10⁻⁵ 11.0 0.92 40.3 4.1 Comparative Polymer 7 18,400 2.16 2.7 × 10⁻⁶ 8.7 0.85 35.4 2.6 Example 1 Comparative Polymer 1 4,500 1.09 1.2 × 10⁻⁵ — — — — Example 2

As seen in the results of Table 1, Examples 1 to 4 (Polymer 3 to Polymer 6), in which the polymer was prepared containing 3,6-carbazole, had 88%, 96%, 65% and 57% improved efficiency, respectively, compared to Comparative Example 1 (Polymer 7), in which the polymer did not contain 3,6-carbazole.

As seen in FIG. 3, and Table 2 that compares the mobility after mixing with PCBM, these results show that, by adding a small amount of 3,6-carbazole having favorable hole mobility to the polymer of Comparative Example 1 (Polymer 7) having unbalanced electron and hole mobility, the hole mobility was improved, and photoelectric conversion efficiency was also improved by achieving balanced electron and hole mobility.

TABLE 2 Category Mobility e/h Comparative Electron Mobility 6.21 × 10⁻⁴ 126 Example 1 Hole Mobility 4.92 × 10⁻⁶ Example 2 Electron Mobility 2.86 × 10⁻⁴ 1.2 Hole Mobility 2.35 × 10⁻⁴

Comparative Example 3 Synthesis of Polymer 8

After 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-dibenzylsilole (200 mg, 0.304 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (139 mg, 0.304 mmol) were dissolved in dried toluene (10 ml), 20% tetraammonium hydroxide solution (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto. The mixture was reacted for 48 hours at 85° C. After the polymerization was complete, the result was polymerized using phenylboronic acid (10 mg) and bromobenzene (1 ml). The reaction product was poured into methanol (200 ml), the precipitate was filtered and then extracted with acetone and hexane/chloroform, and 148 mg of was obtained.

Example 5 Synthesis of Polymer 9

As in the following Reaction Formula 5, in a microwave reaction vial, after 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (21 mg, 0.03 mmol), 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-9,9-dioctyl-9H-dibenzylsilole (162.8 mg, 0.280 mmol) and 4,7-di(2′-bromothien-5′-yl)-2,1,3-benzothiadiazole (143 mg, 0.31 mmol) were placed in dried toluene (3 ml) and 20% aqueous solution of Et₄NOH. Catalyst tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto, the mixture was reacted for 2 hours at 110° C. in a microreactor, and a dark purple solid powder (221 mg), was obtained.

Comparative Example 4 Synthesis of Polymer 10

As in Reaction Formula (6), after 2,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-4,4-dioctyl-4H-cyclopenta[2,1-b;3,4-b′]dithiophene (200 mg, 0.305 mmol) and 3,6-bis(5-bromo-thiophen-2-yl)-2,5-bis-(2-ethyl-hexyl)-2,5-dihydro-pyrrole[3,4-c]pyrrole-1,4-dione (207 mg, 0.305 mmol) were dissolved in dried toluene (10 ml), 20% tetraammonium hydroxide solution (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto. The mixture was reacted for 48 hours at 85° C. After the polymerization was complete, the result was polymerized using phenylboronic acid (10 mg) and bromobenzene (1 ml). The reaction product was poured into methanol (200 ml), the precipitate was filtered and then extracted with acetone and hexane/chloroform, and 256 mg of Polymer 9 was obtained.

Example 6 Synthesis of Polymer 11

In a microwave reaction vial, after 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-heptadecanylcarbazole (21 mg, 0.03 mmol), 2,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-4,4-dioctyl-4H-cyclopenta[2,1-b;3,4-b′]dithiophene (200 mg, 0.27 mmol) and 3,6-bis(5-bromo-thiophen-2-yl)-2,5-bis-(2-ethyl-hexyl)-2,5-dihydro-pyrrole[3,4-c]pyrrole-1,4-dione (207 mg, 0.305 mmol) were placed in dried toluene (3 ml) and 20% aqueous solution of Et₄NOH.

Catalyst tetrakis(triphenylphosphine)palladium(0) (5 mg) and 4 drops of Aliquat 336 were added thereto, the mixture was reacted for 2 hours at 110° C. in a microreactor, and a dark purple solid powder (221 mg), was obtained.

Using the same method as in the manufacture of the organic solar cell and characteristics measurements thereof, an organic photovoltaic device was manufactured using the materials of Example 5 (Polymer 9), Example 6 (Polymer 11), Comparative Example 3 (Polymer 8) and Comparative Example 4 (Polymer 10) as the active payer. J_(sc), V_(oc), FF and PEC were measured for the manufactured device, and results thereof are shown in the following Table 3.

TABLE 3 J_(sc) Mn (mA/ V_(oc) FF PCE Category Polymer (g/mol)^(a) PDI cm²) (V) (%) (%) Comparative Polymer 20,400 2.31 7.4 0.58 0.63 2.7 Example 3  8 Example 5 Polymer 15,400 3.02 8.9 0.59 0.61 3.2  9 Comparative Polymer 13,300 1.44 4.9 0.55 0.57 1.6 Example 4 10 Example 6 Polymer 9,700 1.63 6.5 0.55 0.50 1.8 11

As seen in Table 3, Example 6 (Polymer 9) and Example 7 (Polymer 10), in which the polymer contained a small amount of 3,6-carbazole, had 20% and 23% improved efficiency compared to Comparative Example 3 (Polymer 8) and Comparative Example 4 (Polymer 10), respectively, in which the polymer did not contain 3,6-carbazole. 

1. A copolymer comprising a 3,6-carbazole group represented by the following Chemical Formula 1:

wherein, Y is an electron acceptor; X is an electron donor; Y is represented by the following Chemical Formula:

X is represented by the following Chemical Formula:

R₁ to R₅ are independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl, C₁-C₂₀ heteroaryl, CN, C(O)R or C(O)OR, and R is independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ heterocycloalkyl, aryl or heteroaryl; for l and m, l+m=1 in a molar fraction and m has a range of 0.01≦m≦0.9; and the molecular weight has a range of 5,000≦Mn≦100,000.
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. The copolymer of claim 1, wherein m has a range of 0.01≦m≦0.7.
 6. The copolymer of claim 1, wherein m has a range of 0.01≦m≦0.1, and the copolymer is a conductive copolymer.
 7. 8. An organic solar cell comprising a photoelectric conversion layer, wherein the photoelectric conversion layer comprise an electron acceptor; and a conductive polymer is a copolymer containing a 3,6-carbazole group represented by the following Chemical Formula 1:

wherein, Y is an electron acceptor; X is an electron donor; Y is represented by the following Chemical Formula:

X is represented by the following Chemical Formula:

R₁ to R₅ are independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, C₁-C₂₀ aryl, C₁-C₂₀ heteroaryl, CN, C(O)R or C(O)OR, and R is independently hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ heterocycloalkyl, aryl or heteroaryl; for l and m, l+m=1 in a molar fraction and m has a range of 0.01≦m≦0.7; and a degree of polymerization that ranges from 5 to
 200. 9. The organic solar cell of claim 8, wherein m has a range of 0.01≦m≦0.1.
 10. The organic solar cell of claim 8, wherein the electron acceptor is a C₆₀ fullerene derivative or a C₇₀ fullerene derivative.
 11. The organic solar cell of claim 8, comprising: a substrate; a first electrode formed on the substrate, a photoelectric conversion layer formed on the first electrode; and a second electrode formed on the photoelectric conversion layer.
 12. The organic solar cell of claim 8, wherein m has a range of 0.01≦m≦0.1.
 13. A photoelectric conversion device, comprising a photoelectric conversion material, wherein the photoelectric conversion material includes the conductive copolymer of claim
 1. 14. The photoelectric conversion device of claim 13, which is an organic solar cell, a photovoltaic device, an organic light emitting diode or an organic thin film transistor. 